Laser robot with approach time from origin to a starting position minimized

ABSTRACT

In carrying out precision laser-beam machining by using a laser-beam machining head driven by an additional motion-axis means 8 of a laser robot unit 1, a CPU accommodated in a robot controller 10 calculates time A+B necessary for a laser beam projecting nozzle to travel a distance between a position corresponding to a position of origin OR of a machining locus and a position corresponding to a starting point E on the machining locus at a quick-feed speed, and time C necessary for the laser beam projecting nozzle to travel the same distance in a laser-beam machining mode not including quick-feed operation, compares the times A+B and C, and provides feed motors MA and MB accommodated in the additional motion-axis means 8 with an automatic quick-feed command, when the time A+B is shorter than the time C to thereby enhance an efficiency of the laser machining operation.

TECHNICAL FIELD

The present invention relates to a laser machining method employing amulti-articulated laser:equipped robot having a plurality of axes ofmotion (an axis about which one of the movable elements of an industrialrobot has a degree of freedom of motion is referred to as an axis ofmotion.), and a multi-articulated laser robot provided with a controlapparatus for carrying out the method. More particularly, it relates toa laser-beam machining method that feeds a laser-beam projecting unit,attached to the extremity of a laser robot, by the controlling operationof an additional motion- axis mechanism, incorporating therein two feedmotors, along a narrow machining locus of a small diameter to therebyefficiently machine a workpiece with a laser beam projected through alaser beam projecting nozzle on the laser beam projecting unit, and amulti-articulated laser robot suitable for carrying out the laser-beammachining method.

BACKGROUND ART

A laser robot, particularly a well-known multi-articulated laser robothaving freedom of motion about six axes, is provided with a robot wrist,i.e., one of the movable elements of the robot, attached to theextremity thereof. The robot is further provided with an additional-axismechanism including two drive motors and moves a laser beam projectingunit along a predetermined path, i.e., a feed path, in a biaxialcoordinate plane using the additional motion-axis mechanism. Such alaser robot capable of forming a precision small hole in a workpiece byfeeding the laser beam projecting unit along a circular feed path havinga small diameter has been proposed and put into practical use forlaser-beam machining.

A multi-articulated laser robot provided with the above-mentionedadditional motion-axis mechanism has a robot unit as shown in FIG. 1,and the operation of the robot unit is controlled by a well-known robotcontroller for implementing the desired laser-beam machining.

The robot unit 1 has a robot base 2, a robot body 3 set upright on therobot base 2, a turning robot body 4 turnably joined to the upper partof the robot body 3, a robot upper arm 5 pivotally joined for rotatingabout a horizontal axis to one end of the turning robot body 4, a robotforearm 6 pivotally joined, for rotating about a horizontal axisrelative to the robot upper arm 5, to the extremity of the robot upperarm 5, a robot wrist 7 having three degrees of freedom of motion, joinedto the extremity of the robot forearm 6 and capable of rotatinging aboutthree axes perpendicular to one another in a three-dimensional space,and an additional motion-axis mechanism 8 attached to the robot wrist 7and holding a laser-beam machining head 9 including a laser beamprojecting device that projects a laser beam for laser-beam machining.

The additional motion-axis mechanism 8 is provided with two built-indrive motors, such as servomotors, not shown, and controls thelaser-beam projecting nozzle 9a of the laser-beam machining head 9 formovement, for example, along a desired path in an orthogonal biaxialcoordinate plane according to commands provided by the robot controllerso as to carry out laser-beam machining of a workpiece by the use of alaser beam for cutting, boring and such.

The additional motion-axis mechanism 8 is mainly used as a mechanismspecially for forming small holes with the laser-beam machining head 9.The additional motion-axis mechanism 8 holds the laser beam projectingnozzle 9a at a predetermined position of origin while the movableelements of the six-axis system (the revolving robot body 4, the robotupper arm 5, the robot forearm 6 and the robot wrist 7) of the robotunit 1 are in operation, and the two drive motors of the additionalmotion-axis mechanism 8 are actuated after the laser beam projectingnozzle 9a of the laser-beam machining head 9 has been positioned by therobot unit 1 at the center of a small hole to be formed so as to movethe laser beam projecting nozzle 9a of the laser-beam machining head 9along a machining locus, such as a circular locus, corresponding to thecircumference of the desired small hole to form the small hole bylaser-beam machining.

When feeding the laser beam projecting nozzle 9a of the laser-beammachining head 9 to form such a small hole, the additional-axismechanism 8 positions and stops the laser beam projecting nozzle 9a at aposition of origin, moves the laser beam projecting nozzle 9a for astraight approach travel from the origin position to a positioncorresponding to a point on a desired machining locus, and then feedsthe laser beam projecting nozzle 9a along the desired machining locus tocomplete the operation of laser-beam machining.

Generally, in such a laser-beam machining process, the workpiece isinitially pierced therethrough by a laser beam, and then the laser beamprojecting nozzle 9a is moved along the machining locus to cut theworkpiece by the laser beam. A laser-beam machining method shown in FIG.6 carries out piercing at the position of origin and another laser-beammachining method shown in FIG. 7 carries out piercing at a predeterminedpiercing position near a desired machining locus, such as a positionwhere the edge of a through-hole formed by piercing by the laser beamdoes not cross the machining locus, moves the laser beam for an approachtravel toward the machining locus, and then, moves the laser beam alonga machining locus for laser-beam machining.

The former laser-beam machining method moves the laser beam projectingnozzle 9a of the laser-beam machining head 9 from the position of originto a position corresponding to a point on the desired machining locus ata predetermined comparatively low machining speed along a straight pathfor an approach travel, and then moves the laser beam projecting nozzle9a along the machining locus at a low machining speed for laser-beammachining. Therefore, this laser-beam machining method takes moremachining time and hence the machining efficiency, i.e., machining rate,is rather low.

The latter laser-beam machining method moves the laser beam projectingnozzle 9a at a quick-feed speed from the origin position to thepredetermined piercing position near the desired machining locus,carries out piercing at the piercing position, and then carries outlaser-beam machining at a machining speed lower than the quick-feedspeed. Therefore, this laser-beam machining method is seemingly able tocarry out laser-beam machining at an improved machining efficiency.Practically, it is not necessarily true that the latter laser-beammachining method is able to complete a laser-beam machining process inless time than that required by the former laser-beam machining method,because the latter laser-beam machining method needs to position thelaser beam projecting nozzle 9a at the predetermined piercing positionnear the machining locus and needs to execute more positioningoperations than the former laser-beam machining method.

Accordingly, the selection of either a laser-beam machining method thatstarts laser-beam machining from the position of origin at a lowmachining speed and continues laser-beam machining without increasingthe low machining speed or a laser-beam machining method that moves thelaser beam projecting nozzle at a quick-feed speed from the position oforigin to the predetermined piercing position on the approach path, andthen carries out laser-beam machining at a low machining speed has beendetermined by the operator by a trial-and-error method or by a rule ofthumb. The above-mentioned selection of a laser-beam machining methodhas the inevitable disadvantage that the laser-beam machining cannot becarried out at the highest possible machining efficiency.

The selection of a laser-beam machining method by the operator by atrial-and-error method or by a rule of thumb is an impediment to thepromotion of automation of laser-beam machining by means of a laserrobot.

DISCLOSURE OF THE INVENTION

Accordingly, an object of the present invention is to provide alaser-beam machining method capable of eliminating the disadvantages of,and solving problems encountered in, the conventional laser-beammachining method using the additional motion-axis mechanism of a laserrobot, and a multi-articulated laser robot provided with a control meansenabling implementation of the laser-beam machining method.

Another object of the present invention is to provide a laser-beammachining method capable of automatically carrying out laser-beammachining using the additional motion-axis mechanism on a laser robot ata high machining efficiency, and a control means indispensable forcarrying out the laser-beam machining method of the present invention.

In view of the foregoing objects, when carrying out precision laser-beammachining by moving the laser beam projecting nozzle of a laser-beammachining head (laser beam projecting device), which is positioned andheld beforehand at a position corresponding to a position of origin of amachining locus by the operation of the movable components of the laserrobot, along the machining locus with the two drive motors of theadditional motion-axis mechanism of the laser robot, first the presentinvention calculates the time necessary for moving the laser beamprojecting nozzle along a straight approach path from the positioncorresponding to the origin position to a position corresponding to apoint on the machining locus by a laser-beam machining mode in whichlaser-beam machining is started after carrying out piercing operation atthe original position and the time necessary for moving the laser beamprojecting nozzle along a straight approach path from the positioncorresponding to the origin position to a position corresponding to apoint on the machining locus in another laser-beam machining mode inwhich the laser beam projecting nozzle is moved along a straightapproach path from the position corresponding to the origin position toa position corresponding to a predetermined piercing point on thestraight approach path at a comparatively high quick-feed speed,piercing operation is carried out at the piercing point, and thenlaser-beam machining is carried out at a comparatively low machiningspeed, on the basis of known conditions for the operation of the laserrobot and the additional motion-axis mechanism, including the distancebetween the origin position and the position corresponding to the pointon the desired machining locus, the machining speed, the quick-feedspeed, the time constant corresponding to time necessary for the movingspeed of the laser beam projecting nozzle to increase from zero to thepredetermined machining speed, and the time constant corresponding totime necessary for the moving speed of the laser beam projecting nozzleto increase from zero to the predetermined quick-feed speed, comparesthe calculated necessary times, gives a quick-feed command automaticallyto the additional motion-axis mechanism to carry out laser-beammachining only when the necessary time required by the laser-beammachining mode in which the laser beam projecting nozzle is moved to thepredetermined piercing position at a quick-feed speed is shorter thanthe other necessary time.

The present invention provides a laser-beam machining method that feedsthe laser beam projecting nozzle of a laser robot for a straightapproach travel with two drive motors along a straight approach pathfrom a position corresponding to a predetermined position of origin on aworkpiece to a position corresponding to the starting position of adesired machining locus, and feeds the laser beam projecting nozzle fromthe position corresponding to the starting position along the desiredmachining locus, comprising:

presetting a distance R for the straight approach travel, a quick-feedspeed V0, a machining speed V1, a time constant corresponding to timenecessary for the feed speed to increase from zero to the set quick-feedspeed, and a time constant corresponding to time necessary for themachining speed to increase from zero to the set machining speed asmachining conditions;

calculating first approach time necessary for machining the workpiecewith a laser beam from the position of origin selected as a piercingposition where the laser beam projected through the laser beamprojecting nozzle pierces the workpiece to the starting position on thedesired machining locus at a predetermined machining speed along thestraight approach path, on the basis of the machining conditions;

calculating second approach time necessary for selecting a predeterminedpiercing position near the starting position on the straight approachpath, quick-feeding the laser beam projecting nozzle from a positioncorresponding to the position of origin to a position corresponding tothe predetermined piercing position at a quick-feed speed higher thanthe predetermined machining speed, and carrying out laser beammachining, after piercing the workpiece, from a predetermined point onthe straight approach path to the starting position at the machiningspeed by feeding the laser beam projecting nozzle along a straight pathon the basis of the machining conditions;

comparing the first approach time and the second approach time; and

quickly feeding the laser beam projecting nozzle from the positioncorresponding to the position of origin to the position corresponding tothe predetermined piercing position only when the second approach timeis shorter than the first approach time.

The present invention also provides a multi-articulated industrial robotincluding a multi-articulated robot unit, an additional motion-axismeans for feeding a laser beam projecting nozzle of a laser beamprojecting means provided on the robot unit for a straight approachtravel with two drive motors along a straight approach path from aposition corresponding to a predetermined position of origin on aworkpiece to a position corresponding to a starting position of adesired machining locus, and feeding the laser beam projecting nozzlefrom the position corresponding to the starting position along thedesired machining locus, and control means for controlling the operationof the additional motion-axis means, wherein the control meanscomprises:

a storage means capable of presetting a distance R for the straightapproach travel, a quick-feed speed V0, a machining speed V1, a timeconstant corresponding to time necessary for the feed speed to increasefrom zero to the set quick-feed speed V0, and a time constantcorresponding to time necessary for the machining speed to increase fromzero to the set machining speed V1 for the machining conditions, and ofstoring the preset machining conditions;

a calculating means capable of calculating a first approach timenecessary for machining the workpiece, using a laser beam, from theposition of origin selected as a piercing position where the laser beamprojected through the laser beam projecting nozzle pierces the workpieceto the starting position of the desired machining locus at apredetermined machining speed along a straight path and second approachtime necessary for selecting a predetermined piercing position near thestarting position on the straight approach path, quick-feeding the laserbeam projecting nozzle from a position corresponding to the position oforigin to a position corresponding to the predetermined piercingposition at a quick-feed speed higher than the predetermined machiningspeed, and carrying out laser-beam machining, after piercing theworkpiece, from a predetermined point on the straight approach path tothe starting position at the machining speed by feeding the laser beamprojecting nozzle along a straight path, on the basis of the machiningconditions stored in the storage means; and

a command control means which gives a quick-feed command to the twodrive motors only when the second approach time is shorter than thefirst approach time.

In accordance with the above-mentioned control means, the first approachtime and the second approach time are calculated by the calculatingmeans, and the quick-feed operation is executed automatically accordingto a command provided by the command control means only when the secondapproach time required by a laser-beam machining process includingquick-feed operation is shorter than the first approach time. Therefore,the additional motion-axis means always feeds the laser-beam machininghead with high efficiency and, consequently, laser-beam machining,particularly, precision laser-beam machining for forming a small hole byusing the additional motion-axis means can be achieved with highefficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will be made more apparent hereinafter from the description ofpreferred embodiments thereof with reference to the accompanyingdrawings wherein:

FIG. 1 is a front view illustrating a general construction of a laserrobot unit of a multi-articulated laser robot provided with anadditional motion-axis means;

FIG. 2 is a block diagram of a control means for controlling amulti-articulated laser robot so as to carry out a laser-beam machiningmethod in accordance with the present invention;

FIG. 3 is a diagrammatic view of a locus along which the laser beamprojecting nozzle of a multi-articulated laser robot is moved by anadditional motion-axis means when the laser-beam machining method of thepresent invention is carried out in a laser-beam machining modeincluding quick-feed operation;

FIG. 4 is a diagrammatic view of a locus along which the laser beamprojecting nozzle of a multi-articulated laser robot is moved by anadditional motion-axis means when the laser-beam machining method of thepresent invention is carried out in another laser-beam machining modenot including quick-feed operation;

FIG. 5 is a graphical view illustrating the variation of the movingspeed V of the laser beam projecting nozzle with time, and the timenecessary for the laser beam projecting nozzle to reach a positioncorresponding to a point on a machining locus, for a laser-beammachining mode including quick-feed operation and a laser-beam machiningmode not including quick-feed operation;

FIG. 6 is a diagrammatic view of assistance in explaining a conventionalmethod of feeding a laser beam projecting nozzle in forming a small holeby the laser-beam machining operation of a laser-beam machining headdriven by an additional-axis mechanism; and,

FIG. 7 is a diagrammatic view of assistance in explaining anotherconventional method of feeding a laser beam projecting nozzle in forminga small hole by the laser-beam machining operation of a laser-beammachining head driven by an additional motion-axis means.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to FIG. 2, a robot controller 10 is connected by signal lines,indicated by a line consisting of alternating single long and doubleshort dashes to a robot unit 1 to move or position a laser-beammachining head 9 provided with a laser beam projecting device connectedto an additional-axis mechanism 8 attached to a robot wrist 7 (FIG. 1 )by controlling the operation of the movable components of the robotunit. The robot controller 10 has a built-in first memory (MEMORY 1),i.e., a ROM, storing basic programs for robot control and such, and arewritable second memory (MEMORY 2) i.e., a RAM, for storing laser-beammachining programs entered by operating an input means. The robotcontroller 10 controls the movable components of the robot unit 1through a CPU and an interface 11 according to the programs stored inthe first and second memories.

Machining conditions for precision laser-beam machining, in which thelaser-beam machining head 9 is fed by an additional motion-axismechanism 8 according to the present invention, such as a distance R fora straight approach travel of the laser beam projecting nozzle 9a (FIG.1 ) of the laser-beam machining head 9 between a position correspondingto a position of origin and a position corresponding to a point on amachining locus, a predetermined quick-feed speed V0, a time constantcorresponding to time necessary for feed speed to increase from zero tothe quick-feed speed, and such, for forming a small hole and the likeare stored beforehand in the second memory 2 of the robot controller 10.If required, necessary data can be fetched from the laser-beam machiningprograms during precision laser-beam machining operation; for example, alaser-beam machining speed V1 among those set for the laser-beammachining programs can be used.

The additional motion-axis mechanism 8 is a driving mechanism providedwith two drive motors MA and MB, i.e., servomotors, and is capable ofaccurately controlling the operation for moving the laser-beam machininghead 9 in an orthogonal, biaxial coordinate system. The additional-axismechanism 8 is used for the aforesaid precision laser-beam machining forforming a small hole or the like. This laser-beam machining is moreprecise than the laser-beam machining which can be carried out by movingthe laser-beam machining head 9 along a predetermined machining locus byoperating the movable components of the robot unit 1, i.e., therevolving robot body, the robot upper arm, the robot forearm and therobot wrist of the robot unit 1.

The drive motors MA and MB of the additional motion-axis mechanism 8 arecontrolled by a motor controller 12. The motor controller 12 isconnected to the robot controller 10 and sends control signals to thedrive motors MA and MB of the additional motion-axis mechanism 8according to command signals sent thereto from the robot controller 10.

The enhancement of the efficiency of a laser-beam machining methodaccording to the present invention to be carried out by operating thelaser-beam machining head 9 by the additional motion-axis mechanism 8according to the control operation of the robot controller 10 will bedescribed hereinafter.

FIGS. 3 and 4 show two laser-beam machining modes, in which the movementof the laser-beam machining head 9 is controlled by the additionalmotion-axis mechanism 8, as applied, by way of example, to forming anelliptic hole in a workpiece by laser-beam machining. Naturally, thehighly efficient laser-beam machining method of the present invention isapplicable also to forming holes other than the elliptic hole, such astruly circular holes and square holes.

When the laser beam projecting nozzle 9a of the laser-beam machininghead 9 is to be controlled so as to travel along an elliptic machininglocus F shown in FIGS. 3 and 4, first the movable components of therobot unit 1 are operated to position the laser beam projecting nozzle9a of the laser-beam machining head 9 at a position corresponding to thecentral position OR of the machining locus F. During this laser beamprojecting nozzle positioning operation, the additional motion-axismechanism 8 stops and holds the laser beam projecting nozzle 9a of thelaser-beam machining head 9 at its position of origin using the drivemotors MA and MB.

In the case shown in FIG. 3, the laser beam projecting nozzle 9a ismoved at a quick-feed speed V0 from a position corresponding to thecentral position OR of the machining locus F to a position correspondingto a predetermined point, i.e., a piercing point S, on a straightapproach path having a length corresponding to the distance R, apiercing operation is carried out at the piercing point S, and then thelaser beam projecting nozzle 9a is moved at a machining speed V1 lowerthan the quick-feed speed V0 from the piercing point S to a laser-beammachining starting point E on the machining locus F along a finalapproach section, having a length corresponding to a distance L of theapproach path, and along the machining locus F for laser-beam machining.

In the case shown in FIG. 4, the central position OR of the machininglocus F is used as the piercing point S, piercing is carried out by thelaser beam projected by the laser-beam machining head 9 at the piercingpoint S, and then laser-beam machining is started from the piercingpoint S without moving the laser beam projecting nozzle 9a at thequick-feed speed, to move the laser beam projecting nozzle 9a at theslower machining speed V1 through the laser-beam machining startingpoint E along the machining locus F for laser-beam machining.

In accordance with the present invention, a control means of thecontroller 10 is capable of determining which one of the laser-beammachining modes of FIGS. 3 and 4 should be selected in order to achievehighly efficient laser-beam machining. Usually, the quick-feed speed V0is used only for shifting the laser beam projecting nozzle 9a from onepoint to another and is a comparatively high speed in the range of 100to 200 mm/sec, while the machining speed V1 is used for moving the spotof the laser beam along the machining locus and is a comparatively lowspeed in the order of 30 mm/sec. Naturally, it should be understood thatthese values are not intended to restrict the present invention.

In accordance with the present invention, the approach time necessaryfor the laser beam projecting head 9a to travel from the position oforigin OR of the machining locus F to the laser-beam machining startingpoint E on the machining locus F for each of the laser-beam machiningmodes shown in FIGS. 3 and 4 is calculated, the approach time for thelaser-beam machining mode shown in FIG. 3 and that for the laser-beammachining mode shown in FIG. 4 are compared and examined, and then thelaser-beam machining method is carried out in the laser-beam machiningmode including the quick-feed operation only when the approach timerequired by the laser-beam machining mode including the quick-feedoperation is shorter than that required by the laser-beam machining modenot including the quick-feed operation.

Referring to FIG. 5, in which feed speed is measured on the verticalaxis (ordinate) and time is measured on the horizontal axis (abscissa),the laser-beam machining time necessary for completing the laser-beammachining of the work along the machining locus F in the laser-beammachining mode, indicated by a continuous solid line, including thequick-feed operation in the process of approach travel of the laser beamprojecting nozzle, is A+B. The laser-beam machining time necessary forcompleting the same in the laser-beam machining mode, indicated bydotted line, in which laser-beam machining is started at the position oforigin OR is C. In the present invention, the laser-beam machining timesA+B and C are calculated to make a comparison between them.

In FIG. 5, T1 is time commonly necessary for both cases, i.e., the casewherein the moving speed of the laser-beam machining head 9 held at theposition corresponding to the original position OR is increased fromzero to the predetermined quick-feed speed V0, and the case wherein themoving speed of the laser-beam machining head is increased from zero tothe predetermined machining speed V1. Namely, T1 is a first time.

On the other hand, T2 is time necessary for smoothly accelerating thelaser-beam machining head 9 in the initial stage of acceleration or inthe final stage of raising the moving speed to the predeterminedquick-feed speed V0 or V1 and for smoothly decreasing the accelerationin the decelerating stage of the moving speed of the laser-beammachining head 9 to avoid sharp acceleration and deceleration. Namely,T2 is a second time constant. The time constants T1 and T2 are stored asmachining conditions beforehand in the second memory of the robotcontroller 10.

In the machining mode including the quick-feed operation indicated bythe solid line, the laser beam projecting nozzle 9a needs the time A tomove from the position corresponding to the position of origin OR to thepiercing point S and needs the time B to move at the machining speed V1from the piercing point S to the laser-beam machining starting point Eon the machining locus E after completing piercing. The laser beamprojecting nozzle 9a requires time C to move at the machining speed V1to the laser-beam machining starting point E after completing piercingat the position corresponding to the position of origin OR.

When a conditional expression,

    A+B<C                                                      (1)

is satisfied, it is decided that the quick-feed operation is effective.When a conditional expression,

    A+B≧C                                               (2)

is satisfied, it is decided that the quick-feed operation isineffective.

The CPU of the robot controller calculates the laser-beam machining timeA+B and C on the basis of the data stored in the first and secondmemories. The times A, B and C are calculated by using the followingoperation expressions for different cases as functions of the machiningconditions, i.e., the distances R and L, the predetermined quick-feedspeed V0, the predetermined machining speed V1 and the time constants T1and T2, stored beforehand in the first memory.

Case 1

The moving speed of the laser beam projecting nozzle 9a can be increasedfrom zero to the predetermined quick-feed speed V0 when the laser beamprojecting nozzle 9a is moved in the laser-beam machining mode includingthe quick-feed operation along the straight path from the positioncorresponding to the position of origin OR to the position correspondingto the piercing point S (V0×T1<R-L).

    A=[(R-L)-(V0×T1)/V0]+2×(T1+T2)                 (3)

Case 2

The moving speed of the laser beam projecting nozzle 9a cannot beincreased from zero to the predetermined quick-feed speed V0 when thelaser beam projecting nozzle 9a is moved in the laser-beam machiningmode including the quick-feed operation along the straight path from theposition corresponding to the position of origin OR to the positioncorresponding to the piercing point S (V0×T1≧R-L).

    A=[(R-L)/V0]+T1+(2×T2)                               (4)

Case 3

The moving speed of the laser beam projecting nozzle 9a can be increasedto the predetermined quick-feed speed V when the laser beam projectingnozzle 9a is moved from the position corresponding to the piercing pointS to the position corresponding to the laser-beam machining startingpoint E on the machining locus F in the laser-beam machining modeincluding the quick-feed operation (V1×T1<L).

    B=[L-(V1×T1 )/V1]+2×(T1+T2)                    (5)

Case 4

The moving speed of the laser beam projecting nozzle 9a cannot beincreased to the predetermined quick-feed speed V0 when the laser beamprojecting nozzle 9a is moved from the position corresponding to thepiercing point S to the position corresponding to the laser-beammachining starting point E on the machining locus F in the laser-beammachining mode including the quick-feed operation (V1×T2≧L).

    B=(L/V1)+T1+(2×T2)                                   (6)

Case 5

The moving speed of the laser beam projecting nozzle 9a can be increasedfrom zero to the predetermined machining speed V1 after piercing whenthe laser beam projecting nozzle 9a is moved from the positioncorresponding to the original position OR to the position correspondingto the laser-beam machining starting point E on the machining locus F inthe laser-beam machining mode not including the quick-feed operation(V1×T1<R).

    C=[(R-V1)T1/V1]+2×(T1+T2)                            (7)

Case 6

The moving speed of the laser beam projecting nozzle 9a can be increasedfrom zero to the predetermined machining speed V1 after piercing whenthe laser beam projecting nozzle 9a is moved from the positioncorresponding to the position of origin OR to the position correspondingto the laser-beam machining starting point E on the machining locus F inthe laser-beam machining mode not including the quick-feed operation(V1×T1≧R).

    C=R/V1+T1+(2×T2)                                     (8)

The conditional expressions (1) and (2), and the operation expressions(3) to (8) are stored beforehand in the first memory of the robotcontroller 10, and the machining conditions are stored in the secondmemory. When controlling the feed operation of the additionalmotion-axis mechanism 8 to enable the laser-beam machining head 9 toachieve precision laser-beam machining, the CPU of the robot controller10 executes calculation by using the conditional expressions (1) and (2)to decide whether or not the quick-feed operation is effective and, ifthe quick-feed operation is effective, automatically gives a quick-feedcommand through the interface 11 to the motor controller 12.

If the CPU decided that the quick-feed operation is ineffective, the CPUautomatically provides a machining command requesting the execution ofpiercing at the position of origin OR at a machining speed specified ina laser-beam machining program and the start of laser-beam machining atthe machining speed V0 from that position.

The graph of FIG. 5 used for the foregoing description shows an exampleof the variation of the feed speed V with time T; it may be readilyunderstood that graphs for the cases 2, 4 and 6 are different from thegraph of FIG. 5.

As is apparent from the foregoing description, according to the presentinvention, when carrying out precision laser-beam machining by movingthe laser beam projecting nozzle of the laser-beam machining head, whichis positioned and held beforehand at the position of origin OR of themachining locus by the robot operation of the movable components of thelaser robot, along the machining locus F with the two drive motors MAand MB of the additional motion-axis mechanism of the laser robot, firstthe robot controller calculates the time necessary for moving the laserbeam projecting nozzle along the straight approach path from theposition of origin OR to a position corresponding to a point on themachining locus in a laser-beam machining mode in which laser-beammachining is started after carrying out piercing operation at theoriginal position OR and the time necessary for moving the laser beamprojecting nozzle along a straight approach path from the position oforigin OR to a position corresponding to a point on the machining locusby another laser-beam machining mode in which the laser beam projectingnozzle is moved along a straight approach path from the positioncorresponding to the position of origin OR to a position correspondingto the piercing position on the straight approach path at acomparatively fast quick-feed speed, piercing operation is carried outat the piercing position, and then laser-beam machining is carried outat a comparatively slow machining speed, on the basis of the knownmachining conditions for the operation of the laser robot and theadditional motion-axis mechanism, compares the calculated necessarytimes, and gives a quick-feed command automatically to the additionalmotion-axis mechanism to carry out laser-beam machining only when thenecessary time required by the laser-beam machining mode in which thelaser beam projecting nozzle is moved to the position corresponding tothe predetermined piercing point at the quick-feed speed is shorter thanthe other necessary time. Accordingly, the operator's troublesomedecision, using a trial-and-error method, is unnecessary and theprecision laser-beam machining using the additional motion-axismechanism of the laser robot is carried out automatically in thelaser-beam machining mode including the quick-feed operation, whichgreatly improves the efficiency of the laser-beam machining. When thelaser robot is operated for laser-beam machining, the time necessary forcompleting the machining of a workpiece can be readily curtailedregardless of the skill of the operator.

We claim:
 1. A laser-beam machining method in which a laser beamprojecting nozzle of a laser robot is fed by two feed motors for astraight approach travel along a straight approach path from a positioncorresponding to a predetermined position of origin on a workpiece to aposition corresponding to a starting position of a desired machininglocus, and subsequently the laser beam projecting nozzle is fed from thestarting position along the desired machining locus,comprising:presetting a distance R of the straight approach travel, aquick-feed speed V0, a machining speed V1, respective time constantsindicating respective times necessary for the feed speed to increasefrom zero to the set quick-feed speed, and necessary for the machiningspeed to increase from zero to the set machining speed as machiningconditions; calculating, on the basis of the machining conditions, afirst approach time necessary for machining the workpiece by a laserbeam from the position of origin selected as a piercing position wherethe laser beam projected from the laser beam projecting nozzle piercesthe workpiece to the starting position set on the desired machininglocus at a predetermined machining speed along a straight approach path;calculating, on the basis of the machining conditions, a second approachtime necessary for selecting a predetermined piercing position near thestarting position set on the straight approach path, quick-feeding thelaser beam projecting nozzle from a position corresponding to saidposition of origin to a position corresponding to said predeterminedpiercing position at a quick-feed speed faster than said predeterminedmachining speed, and carrying out laser-beam machining after piercingthe workpiece from a predetermined point on said straight approach pathto said starting position at said machining speed by feeding the laserbeam projecting nozzle along a straight path; comparing said first andsecond approach times; and quick-feeding the laser beam projectingnozzle from the position corresponding to said position of origin to theposition corresponding to said predetermined piercing position only whensaid second approach time is shorter than said first approach time.
 2. Amulti-articulated laser robot including a multi-articulated laser robotunit, and an additional motion-axis means provided with two feed motorsfor feeding the laser beam projecting nozzle of the laser robot unit fora straight approach travel along a straight approach path from aposition corresponding to a predetermined position of origin on aworkpiece to a position corresponding to a starting position on adesired machining locus, and feeding the laser beam projecting nozzlefrom the position corresponding to the starting position along thedesired machining locus, and control means for controlling the operationof the additional motion-axis means, said control means comprising incombination:a storage means capable of storing, as preset machiningconditions, a distance R for said straight approach travel, apredetermined quick-feed speed V0, a predetermined machining speed V1,respective time constants corresponding to respective times necessaryfor a feed speed to increase from zero to said predetermined quick-feedspeed, and necessary for a machining speed to increase from zero to saidpredetermined machining speed; a calculating means capable ofcalculating, on the basis of said machining conditions stored in saidstorage means, a first approach time necessary for machining theworkpiece by a laser beam from said position of origin selected as apiercing position where the laser beam projected from said laser beamprojecting nozzle pierces the workpiece to said starting position onsaid desired machining locus at said predetermined machining speed alonga straight path, and a second approach time necessary for quick-feedingthe laser beam projecting nozzle from a position corresponding to saidposition of origin to a position corresponding to a predeterminedpiercing position at said predetermined quick-feed speed faster thansaid predetermined machining speed by selecting said predeterminedpiercing position at a position near said starting position on saidstraight approach path, and for carrying out the laser-beam machiningafter piercing the workpiece from a predetermined point on the straightapproach path to said starting position at said machining speed byfeeding the laser beam projecting nozzle along a straight path; and acommand control means for providing a quick-feed command to said twodrive motors only when said second approach time is determined to beshorter than said first approach time from comparison of said first andsecond times calculated by said calculating means.
 3. Amulti-articulated laser robot according to claim 2, wherein said storagemeans comprises a random access memory (RAM) arranged so as to berewritten therein.
 4. A multi-articulated laser robot according to claim2, wherein said command control means for providing a quick-feed commandto said two feed motors comprises a motor control means arranged so asto be connected to said calculating means by an interface means.
 5. Amulti-articulated laser robot according to claim 2, wherein said controlmeans is built in and accommodated in a robot control means of saidmulti-articulated laser robot.